Investments (Summary of Amortized Cost and Fair Values of General Obligation and Revenue Bonds) (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Amortized Cost And Estimated Fair Value Of Investment Securities Available For Sale By By Type Of Bonds [Line Items]
Amortized Cost	$ 506,866	$ 504,564
Fair Value	514,466	511,883
States and Political Subdivisions [Member]
Amortized Cost And Estimated Fair Value Of Investment Securities Available For Sale By By Type Of Bonds [Line Items]
Amortized Cost	95,483	98,056
Fair Value	98,717	100,949
General obligation bonds [Member] | States and Political Subdivisions [Member]
Amortized Cost And Estimated Fair Value Of Investment Securities Available For Sale By By Type Of Bonds [Line Items]
Amortized Cost	79,352	78,470
Fair Value	82,110	80,854
General obligation bonds [Member] | States and Political Subdivisions [Member] | California [Member]
Amortized Cost And Estimated Fair Value Of Investment Securities Available For Sale By By Type Of Bonds [Line Items]
Amortized Cost	20,136	20,078
Fair Value	21,484	21,288
General obligation bonds [Member] | States and Political Subdivisions [Member] | Texas [Member]
Amortized Cost And Estimated Fair Value Of Investment Securities Available For Sale By By Type Of Bonds [Line Items]
Amortized Cost	13,472	14,489
Fair Value	13,712	14,675
General obligation bonds [Member] | States and Political Subdivisions [Member] | Illinois [Member]
Amortized Cost And Estimated Fair Value Of Investment Securities Available For Sale By By Type Of Bonds [Line Items]
Amortized Cost	8,608	8,272
Fair Value	8,784	8,394
General obligation bonds [Member] | States and Political Subdivisions [Member] | Ohio [Member]
Amortized Cost And Estimated Fair Value Of Investment Securities Available For Sale By By Type Of Bonds [Line Items]
Amortized Cost	7,870	7,456
Fair Value	7,999	7,555
General obligation bonds [Member] | States and Political Subdivisions [Member] | Washington [Member]
Amortized Cost And Estimated Fair Value Of Investment Securities Available For Sale By By Type Of Bonds [Line Items]
Amortized Cost	5,951	5,966
Fair Value	6,152	6,126
General obligation bonds [Member] | States and Political Subdivisions [Member] | Utah [Member]
Amortized Cost And Estimated Fair Value Of Investment Securities Available For Sale By By Type Of Bonds [Line Items]
Amortized Cost	956	956
Fair Value	985	984
General obligation bonds [Member] | States and Political Subdivisions [Member] | Other [Member]
Amortized Cost And Estimated Fair Value Of Investment Securities Available For Sale By By Type Of Bonds [Line Items]
Amortized Cost	22,359	21,253
Fair Value	22,994	21,832
Revenue bonds [Member]
Amortized Cost And Estimated Fair Value Of Investment Securities Available For Sale By By Type Of Bonds [Line Items]
Amortized Cost	16,131	19,586
Fair Value	16,607	20,095
Revenue bonds [Member] | Water [Member]
Amortized Cost And Estimated Fair Value Of Investment Securities Available For Sale By By Type Of Bonds [Line Items]
Amortized Cost	3,327	7,100
Fair Value	3,437	7,278
Revenue bonds [Member] | College & University [Member]
Amortized Cost And Estimated Fair Value Of Investment Securities Available For Sale By By Type Of Bonds [Line Items]
Amortized Cost	3,220	2,723
Fair Value	3,356	2,834
Revenue bonds [Member] | Sales Tax [Member]
Amortized Cost And Estimated Fair Value Of Investment Securities Available For Sale By By Type Of Bonds [Line Items]
Amortized Cost	2,359	2,361
Fair Value	2,415	2,405
Revenue bonds [Member] | Electric & Power [Member]
Amortized Cost And Estimated Fair Value Of Investment Securities Available For Sale By By Type Of Bonds [Line Items]
Amortized Cost	1,878	1,880
Fair Value	1,914	1,914
Revenue bonds [Member] | Lease [Member]
Amortized Cost And Estimated Fair Value Of Investment Securities Available For Sale By By Type Of Bonds [Line Items]
Amortized Cost	1,356	1,356
Fair Value	1,370	1,362
Revenue bonds [Member] | Other [Member]
Amortized Cost And Estimated Fair Value Of Investment Securities Available For Sale By By Type Of Bonds [Line Items]
Amortized Cost	3,991	4,166
Fair Value	4,115	4,302
Revenue bonds [Member] | States and Political Subdivisions [Member]
Amortized Cost And Estimated Fair Value Of Investment Securities Available For Sale By By Type Of Bonds [Line Items]
Amortized Cost	16,131	19,586
Fair Value	16,607	20,095
Revenue bonds [Member] | States and Political Subdivisions [Member] | California [Member]
Amortized Cost And Estimated Fair Value Of Investment Securities Available For Sale By By Type Of Bonds [Line Items]
Amortized Cost	1,605	2,174
Fair Value	1,650	2,233
Revenue bonds [Member] | States and Political Subdivisions [Member] | Texas [Member]
Amortized Cost And Estimated Fair Value Of Investment Securities Available For Sale By By Type Of Bonds [Line Items]
Amortized Cost	3,768	3,273
Fair Value	3,915	3,387
Revenue bonds [Member] | States and Political Subdivisions [Member] | Illinois [Member]
Amortized Cost And Estimated Fair Value Of Investment Securities Available For Sale By By Type Of Bonds [Line Items]
Amortized Cost	293	294
Fair Value	298	294
Revenue bonds [Member] | States and Political Subdivisions [Member] | Ohio [Member]
Amortized Cost And Estimated Fair Value Of Investment Securities Available For Sale By By Type Of Bonds [Line Items]
Amortized Cost	320	321
Fair Value	328	332
Revenue bonds [Member] | States and Political Subdivisions [Member] | Washington [Member]
Amortized Cost And Estimated Fair Value Of Investment Securities Available For Sale By By Type Of Bonds [Line Items]
Amortized Cost	1,165	1,167
Fair Value	1,194	1,197
Revenue bonds [Member] | States and Political Subdivisions [Member] | Utah [Member]
Amortized Cost And Estimated Fair Value Of Investment Securities Available For Sale By By Type Of Bonds [Line Items]
Amortized Cost	4,167	3,769
Fair Value	4,240	3,834
Revenue bonds [Member] | States and Political Subdivisions [Member] | Other [Member]
Amortized Cost And Estimated Fair Value Of Investment Securities Available For Sale By By Type Of Bonds [Line Items]
Amortized Cost	4,813	8,588
Fair Value	$ 4,982	$ 8,818